1. Field of the Invention
The present invention relates to an engine operated generator and particularly, to an engine operated generator where the number of revolutions of an engine can be controlled in response to a load and a variation in temperature.
2. Description of the Related Art
A lot of engine operated generator used generally as alternating current power sources are equipped with an inverter for stabilizing the output frequency. In such a conventional engine operated generator, an alternating current is generated by a generator driven by an engine, temporally converted into a direct current, and converted back by an inverter to an alternating current output at the commercial frequency before being released. The conventional generator system equipped with the inverter allows its output frequency to be hardly dependent on the number of revolutions of the engine and can determine its output through controlling the number of revolutions of the engine in response to a load.
For example, an inverter equipped engine operated generator is disclosed in Japanese Patent Laid-open Publication (Heisei) 5-18285 where the load is estimated in accordance with an output current from the inverter and used for controlling a throttle opening of the engine. This permits the output voltage of the generator to maintain at substantially a uniform level regardless of variations of the load.
Also, disclosed in Japanese Patent Laid-open Publication (Heisei) 5-146200 is an engine operated generator which can detect its output voltage at the input of an inverter and compare with a predetermined reference voltage to determine the number of revolutions of the engine corresponding to the load.
Applicant of this patent application have proposed an engine operated generator which is equipped with a converter consisted of a semiconductor rectifier element for rectifying the output current of a generator and arranged to control the number of revolutions of the engine so that the conduction angle of the semiconductor rectifier element is converged at a target degree which is smaller than the maximum limit of conduction angle thus to maintain the output voltage of the converter to a desired level (Japanese Patent Laid-open Publication (Heisei) 11-308896). As the generator runs with a moderate margin, it can readily respond to an increase in the load within the margin. Also, the output of the generator can be prevented from being affected by a variation in the number of revolutions of the engine.
It is further desired to improve the conventional generator where the conduction angle of the semiconductor rectifier element is controlled to a target degree which stays smaller than its maximum limit. Generally, the generator is easily affected by the temperature fluctuation. Particularly in a magnet type of the generator having a rotator made of permanent magnets, the magnets develop a magnetic field of higher intensity and the resistance in windings is declined when the temperature is low. As a result, the loss will be minimized. However, when the temperature is high, the magnets develop a magnetic field of lower intensity and the resistance in the windings is increased. Accordingly, the loss will be increased and the output of the system will be lower than at the lower temperature. For an instance, the output may be declined by 10% when the temperature drops down. In that case, while the conduction rate of the semiconductor rectifier element (such as the target degree of the conduction angle of thyristors) remains unchanged, the number of revolutions of the engine at the high temperature can be 10% greater than that at the low temperature.
When the generator having the above characteristics is operated with parameters predetermined for the high temperature, its output remains sufficient at the low temperature regardless of the load. Accordingly, as the conduction angle of the thyristors is not greater than the reference level, the number of revolutions of the engine can hardly be increased. As the number of revolution of the engine is hardly increased to a target level predetermined, the output of the engine will be declined and its action may be overloaded.
It is now assumed that the number of revolutions of the engine is controlled between 3000 and 5000 rpm and the loaded output and the number of revolution of the engine are 1000 VA and 4000 rpm respectively at the normal temperature. When the temperature drops down to xe2x88x9215xc2x0 C., the generator increases the efficiency and its output is higher than at the normal temperature. With the loaded output remaining at 1000 VA, the number of revolutions of the engine will be 3000 to 3200 rpm. Using the number of revolutions smaller than 4000 rpm, the engine may hardly produce electricity of 1000 VA (or be overloaded).
On the contrary, when the temperature is higher than the normal temperature, the generator declines the efficiency and its output is lower than that at the normal temperature. Accordingly, the number of revolutions of the engine will increase excessively. The effect of a variation in the temperature may involve when the generator remains cool, e.g. at the startup, or when the generator remains heated up, e.g. during the continuous running. The characteristic of the number of revolutions may unfavorably be affected by the temperature fluctuation.
It is an object of the present invention to provide an engine operated generator which has a generator arranged to constantly provide its actual performance with a comfortable margin and stably control its output voltage in response to a wider range of electrical load and an engine which drives the generator that is arranged to control the number of revolutions regardless of a variation in the temperature.
The present invention which has the first feature comprises, a converter composed of a semiconductor rectifying element for rectifying the output current of a generator driven by an engine, an inverter for converting a direct current received from the converter into an alternating current at a desired frequency, a semiconductor rectifying element driving circuit for controlling the conduction of the semiconductor rectifying element to adjust the output voltage of the converter to a target level, a conduction rate detecting means for detecting the rate of conduction of the semiconductor rectifying element, an engine revolution controlling means for controlling the number of revolutions of the engine so that the rate of conduction detected by the conduction rate detecting means is converged at a target rate, and a modifying means for modifying the target rate in response to the temperature of the generator.
The present invention which has the second feature that the modifying means is arranged for increasing the target rate when the temperature of the generator is lower than a reference temperature and decreasing the target rate when the temperature of the generator is higher than the reference temperature.
The present invention which has the third feature that the temperature of the generator is represented by the temperature of a power controlling element provided in the inverter.
The present invention which has the fourth feature that the temperature of the generator is represented by the temperature of a power controlling element provided in the converter.
The present invention which has the fifth feature that the rate of conduction is an conduction angle of the semiconductor rectifying element and its target degree is hence a target degree of conduction.
The present invention which has the sixth feature that the generator is a magnet generator.
According to the features of the present invention, the number of revolutions of the engine can be controlled so that the angle or rate of conduction of the semiconductor rectifying element is converged at a target degree predetermined. In particular, when the temperature of the generator is varied, the number of revolutions of the engine can be controlled using a modification of the target degree in response to the output of the generator.
According to the second feature, when the output of the generator increases with the temperature remaining low, the rate of conduction exceeds the target rate early and the number of revolutions of the engine is thus increased quickly. As a result, the engine will hardly be declined in the power output and its overload running will successfully be avoided. When the output of the generator increases with the temperature remaining high, the rate exceeds the target rate slowly and the increase of the number of revolutions of the engine is delayed. As a result, the engine will be inhibited from running at an excessively higher number of revolutions.
According to the third feature, the rate of conduction can be modified depending on the temperature of the power controlling element provided in the inverter or converter which positively represents the temperature of the generator. Also, according to the fourth feature, the conduction angle of the semiconductor rectifying element can be modified depending on the temperature of the generator. According to the fifth feature, the effect of a variation in the magnetic field developed by the permanent magnets which is caused by a variation in the temperature will be minimized.